GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 285 



the mouths of the streams, either by growing up to the edges of the 

 outflowing water, a channel thereby being maintained, or because of 

 their greater hardness they offered greater resistance to erosion than 

 did the softer rocks on their landward side. It is my present 

 opinion that the hypothesis of the reefs having more than a secondary 

 importance in the development of these featm*es must be discarded 

 for the following reasons: First, that such physiographic forms are 

 in no wise dependent on the presence of coral reefs is shown by their 

 frequency in areas underlain by Cretaceous limestones in Texas. 

 Hillcoat Valley in the southwest quarter of the Nueces quadrangle, 

 Texas, is such a basin, with a narrow outlet into Nueces Kiver. This 

 is only one of a number of instances that might be given. In phy- 

 siographic form this basin and its outlet resemble the pouch-shaped 

 harbors of Cuba. Second, there is no evidence that corals had any 

 more influence in Cuba than in Texas, for instance, Yumuri gorge at 

 Matanzas is about 200 feet deep. The highest important elevated coral 

 reef rocks occur at an altitude of about 35 feet above sea level off the 

 sides of the stream mouth. The stream has cut and maintained a gorge 

 through about 165 feet of limestone and marl which are topographi- 

 cally above the reef and which are not coral reef rocks, but which 

 are bedded and were formed by other agencies. Other instances of 

 these relations might be given. 



The conditions around the Habana Harbor are interesting in this 

 connection. Limestone of upper OUgocene or Miocene age occurs 

 at the Morro and forms the higher land along the shore east of the 

 city, and it outcrops at lower altitudes in the western part of the 

 city; but the drainage at the south end of the harbor has cut through 

 the limestone and exposed the imderlying rocks, serpentine, rotten 

 diorite, etc.; and that undergroimd solution is active is indicated by 

 the presence of springs along the serpentine contact. The condi- 

 tions are here favorable for erosion by both mechanical cutting and 

 solution in the area lying behind, while a channel has been main- 

 tained across the limestone on the sea front. This basin after it 

 was outlined was submerged. 



It is intended to give a much fuller discussion of the Cuban harbors 

 in a paper now almost ready for press. The differences in form, and 

 the causes to which the differences are due, are worthy of far more 

 detailed treatment than is practicable in this place. I will end this 

 part of the present discussion by saying that corals have in certain 

 instances played a subordinate role by narrowing the mouth of a 

 harbor and by preserving a constricted outlet. That the outlets of 

 the basins here considered were constricted by reef rocks, now ele- 

 vated, is shown by the conditions in Habana and Santiago harbors, 

 and that similar constriction is now taking place by similar agencies 



